The present invention is in the field of motor controllers. More specifically, the present invention is in the field of stepper motor controllers.
Stepper motors are currently used in a variety of applications, including moving paper of fabric or other material along a manufacturing assembly line. The motors are often controlled by microprocessors, which time the movement of the material along the assembly line and control other equipment based on the anticipated timed movement of the material along the assembly line. If one of the motors slips or stalls of otherwise fails to perform the task of moving the material along the assembly line, either the other equipment will continue to run damaging a portion of the material along the assembly line or the motors will stop until the system is reset. Both of these results are costly and many devices have been developed over the years to avoid the problematic slips and stalls.
Another problem caused by slips and stalls is a loss of motor efficiency. The most problematic time for the motors is when they are ramping up to full speed and capacity. During the ramping time, which is relatively brief, the material is moved is moved and processed along the assembly line at an escalating rate. Once ramping is completed, the material is moved along the assembly line at a constant speed, substantially reducing the risk of slips or stalling. Several devices have been designed to increase motor efficiency during ramping, but none can reactively prevent slips or stalling in real-time while the motors are ramping.
Finally, some materials have more problems being moved across assembly lines than others do. Felt, for instance, is a material with an inconsistent frictional coefficient. As a result, the felt is likely to slip when being pulled by the motors, particularly during the ramping up of the system, which can result in either the material being damaged or the motors being shut down, as previously explained. Therefore assembly lines that move materials with low and/or inconsistent frictional coefficients suffer greater inefficiency than other assembly lines.
The present invention is directed to a very specific problem. Along an assembly line for moving felt, there are stepper motors for moving the felt a preprogrammed distance repeatedly, The stepper motors rotate pinch roller assemblies a preprogrammed angular rotation relative to the preprogrammed distance. The anticipated result is the pinch roller assemblies move the felt the preprogrammed distance. However if the pinch roller assemblies insufficiently grip the felt, as is prone to happen with a material having a low frictional coefficient, the felt moves less than the preprogrammed distance. Another device is then initiated to manipulate a section of feltxe2x80x94punching holes, attaching something to the felt or otherwise manipulating it. The preprogrammed distance is directly related to an intended spacing between manipulations of sections of felt. Therefore, when the felt fails to move the intended distance, the intended spacing is not achieved.
The present invention is the realization that the motors in an assembly line can be more efficiently controlled if the timing of the motors is based on the real-time tracking of the speed of the material moving across the assembly line, particularly during the ramping up or down of the motors. The present invention uses an encoder, which mechanically tracks the speed and position of the material moving across the assembly line and translates the speed and position to electrical signals. Those electrical signals modify the timing of the motors and other devices along the assembly line.
An issue resolved by the present invention is to provide a drive system that uses an encoder to monitor and control the feed distance. Because the encoder has direct control of the system execution, each feed advance builds unique, real-time acceleration and deceleration curves. This type of direct system execution automatically compensates for losses due to friction, slippage or missed steps from the stepper motors. This approach more than doubles the speed and accuracy of the feed process over conventional systems using the same motors, feed path and material being fed.
Therefore, it is an object of the present invention to cause the assembly line to automatically correct for motor stalls or slippage rather than stopping the assembly line or damaging the material being moved along the assembly line.
It is a further object of the present invention to increase the efficiency during ramping by reacting to the increasing speed with which the material is moved across the assembly line rather than being programmed to anticipate expected speed increases.
Finally, it is a further object of the present invention to greatly increase the efficiency of assembly lines, which move materials with low and/or inconsistent frictional coefficients across the assembly line.